Measuring the Nutritive Content of a Foraging Sheep's Diet under Range Conditions

Abstract

Need for an understanding of the nutrition problems on the western range is of paramount importance. Despite the importance of this problem, little is known as to the actual composition of the grazing animal's diet. The reasons for this lack of knowledge are many fold, including (a) difficulty of collecting representative samples of vegetation because of soil, site, and seasonal variations, (b) difficulty of finding what species and portions of plants actually are consumed, and (c) difficulty in interpreting the nutritive content of the ingested forage. The method here presented for determining the nutritive content of the sheep's diet under range conditions is an entirely new approach to this problem and is based upon chemical analyses of the vegetation before being grazed as compared to chemical analyses after being grazed. Briefly, the method consists of collecting a predetermined number of plant units before grazing and a similar number after grazing. Each plant species is sampled both before and after grazing and each sample is weighed and chemically analyzed. The difference in weight and chemical composition between the before-grazing sample and the after-grazing sample serves as a measure of the nutrient content of the ingested forage. It was found from this study that sheep are highly selective in their diet and consume largely leaves and tender stems, rejecting the more fibrous parts of the plant. Consequently, a much better quality of forage actually makes up the diet than chemical analyses of bulk samples would indicate.